1. Field
The embodiments discussed herein are directed to a contactless information storage device of active type capable of reading and writing information in a contactless manner and, in particular, to an RFID tag or a contactless IC card of active type and of low power consumption that has a sensor and accumulates detected values from the sensor.
2. Description of the Related Art
An RFID tag of active type, that is, of battery-powered type, is attached to a product or the like or carried by a person, and then transmits an RF signal at a predetermined frequency that carries an ID and information concerning the product or the person. This RF signal is read by a reader device.
The read information is further processed by a computer and the like. Then, the distribution of the product or the action of the person can be monitored and managed.
The active-type RFID tag powered by a battery has a rather long communication-reachable distance and hence is practical in comparison with a passive-type RFID tag that receives electric power from a reader/writer device in a contactless manner.
Nevertheless, the active-type RFID tag transmits RF signals with a constant period, and hence has a risk of being tracked by a third party. This causes a problem in security.
As a security measure against this, an improved active-type RFID tag is known that responds only to a tag ID request from a reader/writer device.
When an active RFID tag that has a sensor for detecting a physical quantity in the surrounding environment and that accumulates the data of a plurality of such detected values is read by a reader/writer device, detected value data can be collected together with an ID.
Conventionally, an IC tag detection system of low power consumption includes a communication circuit; a control section; a power supply section for supplying electric power to these from a battery; and a time counter. The system further comprises: a plurality of IC tags which perform transmission at each predetermined setting time of day and in which their setting time of day is different from each other; and a detector for detecting the presence or absence of each tag based on communication with each tag. The detector has a communication circuit. Then, the presence or absence of receiving is determined successively at each setting time of day of each IC tag so that detection is performed.
Since no inquiry is performed from the detector, the IC tag can avoid useless reactions and battery exhaustion.
Conventionally, a method of realizing frequency locking does not require separate reference oscillators each in a transmitter in each of two nodes in a duplex link.
In a full duplex link, the carrier frequencies of transmitters are tuned by using information concerning a received frequency, so that the transmission frequencies of the two nodes in the link are locked simultaneously.
The offset in the carrier frequency of a first transmitter is detected as an offset in a corresponding second receiver.
The second receiver shifts the carrier frequency of the transmitter in accordance with the detected offset, and then notifies the detected offset to the first transmitter.
The carrier frequency of the transmitter is corrected in accordance with the offset detected in the first receiver.
Conventionally, a system monitors the pressure in a pneumatic tire of an automobile and transmitting a signal by wireless.
This system monitors the pressure or a pressure variation in a pneumatic tire of a wheel of an automobile and transmits a signal by wireless.
The system comprises: a receiver unit provided in the automobile and having at least one antenna; and a unit provided in a pneumatic tire and measuring, evaluating and transmitting a tire pressure signal.
When the pressure variation does not exceed a threshold, the transmitter unit does not transmit a pressure signal. Thus, electricity is saved.
Conventionally, a monitoring terminal device includes: a sensor section; and a transfer section having a wireless communication function of transmitting a sensor monitor output by wireless.
In the monitoring terminal device, the sensor and the wireless transmitter are operated intermittently. Thus, at the time of non-operating, electric power to the sensor section and the transfer section is turned OFF, and further the control processor is brought into a sleep state, so that power consumption is reduced.
Accordingly, even under an environment where electric power cannot be obtained from the outside, long-term operation is ensured.
Conventionally, in a tag system, a tag reader periodically transmits to an IC tag a beacon signal containing a command or an ID. The IC tag detects the command or the ID contained in the beacon signal received from the tag reader, then judges an operating condition based on the command or the ID, and then changes the own operation of the IC tag (e.g., an activation period).
By virtue of this, the probability of conflict of signals caused by an increase in the density of the IC tags is reduced. Further, the power consumption of the IC tag is reduced. Furthermore, when security service is necessary, rapid warning can be issued.
In the above-mentioned conventional system, regardless of the remaining power level of the battery, a signal is transmitted depending on whether the amount of variation in the measured value exceeds a threshold. Then, when the remaining battery power level goes insufficient, the system stops suddenly.
Further, for the purpose of reduce the power consumption, when the period of physical quantity detection and carrier sensing in the RFID tag is set to be longer so that the sleep duration is extended, the RFID tag cannot transmit back a response to a request command from an approached reader/writer device in a short time.